1. Field of the Invention
The invention relates to a gearbox for a motor vehicle.
The invention relates more particularly to a motor-vehicle gearbox of the type provided with at least two longitudinal parallel shafts, the primary and secondary, of the type provided with at least two gear pairs, in each of which an idler pinion, mounted to rotate on a first shaft, engages with a fixed pinion supported by a second shaft, and of the type provided with means for interlocking each idler pinion on its shaft by means of axially movable coaxial bands, under the action of operating means provided with operating forks which are mounted to slide in parallel on the shafts, each of which forks is equipped with a transverse foot, at the end of which there is provided a contact toe, the toes being aligned transversely along an arc of a circle to be received in a yoke of an actuator which can be driven in transverse displacement along the arc of the circle to select a fork associated with a gear reduction ratio, and parallel to the shafts to engage the ratio associated with the selected fork by longitudinally displacing a band for interlocking of the idler pinion corresponding to this ratio.
2. Discussion of the Background
There are known numerous gearboxes provided with operating means for interlocking of idler pinions on the shafts supporting them, in such a manner as to cause their engagement with the associated fixed pinions belonging to at least one other shaft and thus selectively to engage specified gear reduction ratios associated with the said idler pinions.
Motor-vehicle gearboxes conventionally rely on interlocking devices with synchronizers of the type of those cited hereinabove, the said synchronizers being capable of being axially displaced by the forks supported by axles, and being capable of being actuated longitudinally the vehicle driver by means of a gear change lever disposed in the passenger compartment of the vehicle. In the case of a xe2x80x9cmanualxe2x80x9d gearbox, the gear change lever actuates a rod assembly which acts directly on the forks, and in the case of a xe2x80x9crobotizedxe2x80x9d or automatic gearbox, the gear change lever indirectly drives the displacement of the forks, especially by means of hydraulic cylinders or other types of actuators.
French Patent Application A 2609138 describes such a device.
That document describes more particularly an architecture for an automatic gearbox in which interlocking of the idler pinions on their shaft and displacement of the synchronizers parallel to this shaft is achieved by forks displaced by actuators, in this case hydraulic cylinders. Each fork is displaced by an associated actuator.
This arrangement is particularly bulky, because it necessitates a large number of forks, fork axles and actuators.
To reduce the space requirement of such devices and to reduce the manufacturing costs, it has been proposed that there be used only a single actuator capable of consecutively driving the displacements of a plurality of forks.
Such a device is described in German Patent Application DE A 3600185.
In that device, an actuator is provided with an arm, at the end of which a toe is capable of being displaced in rotation and in translation respectively to select a fork and engage a ratio associated with the fork in question by displacing it parallel to the shaft of the gearbox.
The described device has a certain advantage compared with the preceding device to the extent that the number of actuators is considerably reduced. Nevertheless, it remains very bulky because of the multiplicity of fork axles and of their arrangement in which they are distributed transversely.
To remedy these disadvantages, the invention proposes to improve the compactness of the gearbox by reducing its transverse space requirement.
For this purpose, the invention proposes a gearbox of the type mentioned hereinabove, characterized in that all operating forks are mounted to slide on a common fork axle, parallel to the shafts.
According to other characteristics of the invention:
at most one interlocking band is provided close to an idler pinion, to occupy selectively a neutral position or an interlocked position of the single pinion in question, the said interlocked position corresponding to engagement of a gear reduction ratio, and in that the other interlocking bands are provided between two idler pinions, to occupy a neutral position or two opposite interlocked positions of each of the idler pinions in question, the said interlocked positions being situated axially on the two sides of the neutral position and each corresponding to engagement of a gear reduction ratio;
the actuator is provided with a rod, longitudinal and parallel to the shafts, which is provided with a transverse arm, at the end of which there is provided the yoke, which can occupy a plurality of predefined angular selection positions, each of which corresponds to selection of a fork, and at least two predefined longitudinal shift positions, which comprise at least one extreme longitudinal position of engagement of one of the gear reduction ratios and a neutral position;
the fork axle is coaxial with the rod of the actuator;
the idler pinions and the associated interlocking bands are provided axially on the first shaft of the gearbox;
the gearbox is a box with robotized operation and the actuator is a rotolinear hydraulic cylinder moved by stepping motors, driven in response to movements of a vehicle gear change lever on which the driver acts;
the gearbox is operated manually and the actuator is linked by a rod assembly to the vehicle gear change lever on which the driver acts.